Woodlands and forestlands are composed of an overstory of tree canopy and an understory that is divided into shrub and forb layers. These plant communities occur in many diverse regions. They function as wildlife habitat, modulators of hydrologic flow, and protectors of soil. Forests provide a diverse range of resources including storing carbon, regulating climate, purifying water and preventing hazards such as floods. Through the development of plants and technology, the Plant Materials Program provides resources for establishing and maintaining the forest ecosystem.